Water-swellable polymers are used as constituents in personal care materials which absorb bodily fluids such as disposable baby diapers, sanitary napkins, and incontinent devices. U.S. Pat. Nos. 3,926,891, 4,190,562, and 4,293,609, the relevant portions incorporated herein by reference, provides examples of such polymers.
Various processes are known for producing water-swellable polymers. For example, U.S. Pat. No. 4,833,222, the relevant portions of which are incorporated herein by reference, teaches a process for preparing an absorbent polymer from a neutralized monomer in the absence of a surface active agent. U.S. patent application Ser. No. 756,731 discloses a process for preparing a water-swellable polymer having improved absorptive properties, the relevant portions of which are incorporated herein by reference.
U.S. Pat. No. Re. 32,649, discloses a process for producing absorbent polymers comprising preparing a reaction mixture consisting essentially of particular amounts of polymerizable acid group-containing monomers, crosslinking agents, and free radical initiator, in an aqueous medium, and thereafter polymerizing and neutralizing at least a portion of the acid functional groups.
Absorbent polymers used in personal care devices must absorb liquid under a variety of pressures. For instance, the polymer in a disposable baby diaper will preferably absorb freely when the baby is standing, but must likewise absorb under pressure when the baby is sitting. Properties such as absorbency under load and capacity reflect the absorptive properties of the polymer.
In addition to preferred absorptive properties, the water-swellable polymer will preferably not detract from the aesthetic design of the personal care device in which it is incorporated. In particular, water-swellable polymers which are white rather than yellowed, have greater commercial appeal.
Water-swellable polymers may incorporate polyvinyl alcohols. However, it has been found, that certain types of polyvinyl alcohols impart a yellow tone to the water-swellable polymers in which they are incorporated.
Those in the industry would find great advantage in a water-swellable polymer containing polyvinyl alcohols which is suitably white, rendering such water-swellable polymers especially preferred in personal care articles.